A port throttled engine may provide fuel efficiency and/or performance benefits as compared to engines that are not port throttled. However, it may be more difficult to determine cylinder air charge or trapped mass of a port throttled engine when cylinder air trapped mass of the port throttled engine is estimated based on an intake manifold pressure sensor that is positioned upstream of the port throttle or when the engine has a mass air flow sensor positioned upstream of the port throttle. In particular, a manifold absolute pressure sensor (MAP) may not be subject to the pressure at the cylinder intake port. As such, a cylinder air trapped mass estimated from the MAP sensor may not be as accurate as is desired. Even a MAP sensor positioned downstream of the port throttle may provide in accurate cylinder air trapped mass estimates with conventional signal processing due to large pressure fluctuations during each engine cycle. Further, a cylinder air trapped mass estimate that is based on a mass airflow sensor positioned upstream of the port throttle may not provide as accurate cylinder air trapped mass estimates as is desired during transient changes in intake manifold pressure due to the remoteness of the mass air flow sensor.
The inventors herein have recognized the above-mentioned limitations and have developed a method of sampling, a method of sampling, comprising: sampling a sensor positioned in an intake port downstream of a port throttle, the intake port leading to a single cylinder, the sensor sampled at a first time and a second time during a cycle of the single cylinder; and adjusting a first actuator responsive to a first sample taken at the first time and adjusting a second actuator responsive to a second sample taken at the second time.
By positioning a pressure sensor between an intake valve of a cylinder and a port throttle it may be possible to accurately determine MAP and trapped mass of a cylinder. In particular, if a sensor positioned between an intake poppet valve of a cylinder and a port throttle that regulates air flow to an individual cylinder is sampled near intake valve closing (IVC) time as well as just before intake valve opening (IVO) time, cylinder trapped mass may be determined via the first sample while MAP may be determined via the second sample. The mass trapped in the cylinder during a combustion cycle may be more accurately determined when the sensor is sampled near IVC since cylinder intake port pressure at that time is close to cylinder pressure. Further, engine MAP may be accurately determined without locating a MAP sensor in the intake manifold via sampling the intake port sensor at a time where pressure in the cylinder intake port has time to recover and approach or reach MAP. Thus, at least two different control variables may be more accurately determined from two or more different samples taken during a cylinder cycle. Further, the timing at which the samples are taken may act to improve estimation of control variables from which actuators may be adjusted.
The present description may provide several advantages. Specifically, the approach may improve estimates of MAP, cylinder trapped mass, and exhaust pressure. Further, the approach may reduce the number of samples used to determine multiple control variables. In addition, strategically determined sample times may reduce signal processing timing.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.